Color plus clear coatings employing polyepoxides and polyacid curing agents

ABSTRACT

A color-plus-clear coating system is disclosed. A pigmented or colored base coat is first applied to a substrate followed by the application of a transparent top coat to the base coat. Either the transparent top coat, the base coat or both the top coat and base coat compositions are crosslinkable compositions comprising a polyepoxide and a polyacid curing agent which comprises a half-ester formed from reacting an acid anhydride with a polyol. The polyepoxide-polyacid curing agent in the transparent top coat provides a composite coating with outstanding gloss and distinctness of image making the composite coating particularly useful as an automotive top coat.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to application Ser. No. 767,019, filed on Aug. 19,1985. This application claims liquid crosslinkable compositions whichare useful in the process of the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to a process for preparing multi-layeredcoated articles comprising a pigmented or colored base coat and atransparent or clear top coat, and to the coated articles themselves.

2. Brief Description of the Prior Art:

Color-plus-clear coating systems involving the application of a coloredor pigmented base coat to a substrate followed by the application of atransparent or clear top coat to the base coat are becoming increasinglypopular as original finishes for automobiles. The color-plus-clearsystems have outstanding gloss and distinctness of image, and the clearcoat is particularly important for these properties. Two-pack clear coatcompositions comprising polyols such as polyester polyols, polyurethanepolyols and acrylic polyols and polyisocyanate curing agents giveoutstanding gloss and distinctness of image. However, thepolyisocyanates are difficult to handle being sensitive to moisture andrequire cumbersome safety precautions.

It is an object of the present invention to provide a color-plus-clearcoating system which avoids the problems of polyisocyanate curing agentsbut which provides a finish which has outstanding gloss and distinctnessof image so that the coating is useful as an original finish forautomobiles.

SUMMARY OF THE INVENTION

In accordance with the present invention, a process for applying acomposite coating to a substrate is provided. The process comprisesapplying to the substrate a film-forming composition to form a base coatand applying to the base coat a film-forming composition to form atransparent top coat over the base coat. Either the base coat, thetransparent top coat or both the base and top coats are derived from acrosslinkable composition comprising a polyepoxide and a polyacid curingagent which comprises a half-ester formed from reacting an acidanhydride with a polyol. The curing agent can be tailor made withspecific anhydrides and polyols without forming high molecular weightmaterials enabling the formulation of high solids coating compositionswhich provide cured coatings with excellent gloss and distinctness ofimage. The invention also provides for the resultantly coated article.

DETAILED DESCRIPTION

The film-forming composition of the base coat can be any of thecompositions useful in coatings applications, particularly automotiveapplications. The film-forming composition comprises a resinous binderand a pigment to act as the colorant. Particularly useful resinousbinders are acrylic polymers, polyesters, including alkyds, andpolyurethanes.

The acrylic polymers are copolymers of one or more alkyl esters ofacrylic acid or methacrylic acid optionally together with one or moreother polymerizable ethylenically unsaturated monomers. These polymersmay be either of the thermoplastic type or thermosetting crosslinkingtype. Suitable alkyl esters of acrylic acid or methacrylic acid includemethyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylacrylate, butyl acrylate and 2-ethylhexyl acrylate. Suitable othercopolymerizable ethylenically unsaturated monomers include vinylaromatic compounds such as styrene and vinyl toluene; nitriles such asacrylonitrile and methacrylonitrile; vinyl and vinylidene halides suchas vinyl chloride and vinylidene fluoride and vinyl esters such as vinylacetate.

Where the polymer is of the crosslinking type, suitable functionalmonomers may be used in addition to the other acrylic monomers mentionedabove and include, for example, acrylic acid, methacrylic acid,hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylacrylate, and hydroxypropyl methacrylate. The coating composition insuch cases contains a crosslinking agent such as a condensate of anamine or an amide with formaldehyde such as urea, melamine, orbenzoguanamine reacted with formaldehyde or a lower alkyl ether of suchcondensate in which the alkyl groups contain from 1 to 4 carbon atoms.Other crosslinking agents such as polyisocyanates including blockedpolyisocyanates may also be used. Also, the acrylic polymer can beprepared with N-(alkoxymethyl)-acrylamides andN-(alkoxymethyl)methacrylamides which result in self-crosslinkingacrylic polymers.

The acrylic polymer may be prepared by solution polymerizationtechniques in the presence of suitable catalysts such as organicperoxides or azo compounds, for example, benzoyl peroxide orN,N'-azobis(isobutyronitrile). The polymerization can be carried out inan organic solution in which the monomers are soluble. Suitable solventsare aromatic solvents such as xylene and toluene and ketones such asmethyl amyl ketone. Alternately, the acrylic polymer may be prepared byaqueous emulsion or dispersion polymerization techniques.

Besides acrylic polymers, the resinous binder for the base coatcomposition may be an alkyd resin or a polyester. Such polymers may beprepared in a known manner by condensation of polyhydric alcohols andpolycarboxylic acids. Suitable polyhydric alcohols include ethyleneglycol, propylene glycol, butylene glycol, 1,6-hexylene glycol,neopentyl glycol, diethylene glycol, glycerol, trimethylolpropane, andpentaerythritol.

Suitable polycarboxylic acids include succinic acid, adipic acid,azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid,tetrahydrophthalic acid, hexahydrophthalic acid, and trimellitic acid.Besides the polycarboxylic acids mentioned above, functional equivalentsof the polycarboxylic acids such as anhydrides where they exist or loweralkyl esters of the polycarboxylic acids such as the methyl esters maybe used.

Where it is desired to produce air-drying alkyd resins, suitable dryingoil fatty acids may be used and include those derived from linseed oil,soya bean oil, tall oil, dehydrated castor oil or tung oil.

The polyesters and preferably the alkyd resins contain a portion of freehydroxyl and/or carboxyl groups which are available for furthercrosslinking reaction. Suitable crosslinking agents are the amine oramide-aldehyde condensates or the polyisocyanate curing agents asmentioned above.

Polyurethanes can also be used as the resinous binder of the base coat.Among the polyurethanes which can be used are polymeric polyols whichare prepared by reacting the polyester polyols or acrylic polyols suchas those mentioned above with a polyisocyanate such that the OH/NCOequivalent ratio is greater than 1:1 so that free hydroxyl groups arepresent in the product.

The organic polyisocyanate which is used to prepare the polyurethanepolyol can be an aliphatic or an aromatic polyisocyanate or a mixture ofthe two. Diisocyanates are preferred, although higher polyisocyanatescan be used in place of or in combination with diisocyanates.

Examples of suitable aromatic diisocyanates are 4,4'-diphenylmethanediisocyanate and toluene diisocyanate. Examples of suitable aliphaticdiisocyanates are straight chain aliphatic diisocyanates such as1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates canbe employed. Examples include isophorone diisocyanate and4,4'-methylene-bis-(cyclohexyl isocyanate). Examples of suitable higherpolyisocyanates are 1,2,4-benzene triisocyanate and polymethylenepolyphenyl isocyanate.

Most of the polymers prepared as described above are organicsolvent-based polymers, although acrylic polymers can be prepared viaaqueous emulsion polymerization techniques and used as aqueous-basedbase coat compositions. Water-based base coats in color-plus-clearcompositions are disclosed in U.S. Pat. No. 4,403,003, and the resinouscompositions used in preparing these base coats can be used in thepractice of this invention. Also, water-based polyurethanes such asthose prepared in accordance with U.S. Pat. No. 4,147,679 can be used asthe resinous binder in the base coat.

The resinous binder for the base coat can also be the resinous binderused in formulating the clear film-forming composition described below.

The base coat composition also contains pigments to give it color.Compositions containing metallic flake pigmentation are useful for theproduction of so-called "glamour metallic" finishes chiefly upon thesurface of automobile bodies. Proper orientation of the metallicpigments results in a lustrous shiny appearance with excellent flop,distinctness of image and high gloss. By flop is meant the visual changein brightness or lightness of the metallic coating with a change inviewing angle, that is, a change from 90° to 180°. The greater thechange, that is, from light to dark appearance, the better the flop.Flop is important because it accentuates the lines of a curved surfacesuch as on an automobile body. Suitable metallic pigments include inparticular aluminum flake, copper bronze flake and mica.

Besides the metallic pigments, the base coating compositions of thepresent invention may contain non-metallic color pigments conventionallyused in the surface coating compositions including inorganic pigmentssuch as titanium dioxide, iron oxide, chromium oxide, lead chromate andcarbon black, and organic pigments such as phthalocyanine blue andphthalocyanine green. In general, the pigment is incorporated into thecoating composition in amounts of about 1 to 80 percent by weight basedon weight of coating solids. The metallic pigment is employed in amountsof about 0.5 to 25 percent by weight of the aforesaid aggregate weight.

If desired, the base coat composition may additionally contain othermaterials well known in the art of formulated surface coatings. Thesewould include surfactants, flow control agents, thixotropic agents,fillers, anti-gassing agents, organic co-solvents, catalysts and othercustomary auxiliaries. These materials can constitute up to 40 percentby weight of the total weight of the coating composition.

The base coating compositions can be applied to various substrates towhich they adhere. The compositions can be applied by conventional meansincluding brushing, dipping, flow coating, spraying and the like, butthey are most often applied by spraying. The usual spray techniques andequipment for air spraying and electrostatic spraying and either manualor automatic methods can be used.

Coatings of the present invention can be applied over virtually anysubstrate including wood, metals, glass, cloth, plastic, foam, includingelastomeric substrates, and the like. They are particularly useful inapplying over metal and elastomeric substrates that are found on motorvehicles.

During application of the base coat composition to the substrate, a filmof the base coat is formed on the substrate. Typically, the base coatthickness will be about 0.01 to 5, preferably 0.1 to 2 mils inthickness.

After application to the substrate of the base coat composition, a filmis formed on the surface of the substrate. This is achieved by drivingsolvent, i.e., organic solvent or water, out of the base coat film byheating or simply by an air-drying period. Preferably, the heating stepwill only be sufficient and for a short period of time to insure thatthe top coat composition can be applied to the base coat without theformer dissolving the base coat composition, i.e., "striking in".Suitable drying conditions will depend on the particular base coatcomposition, on the ambient humidity with certain water-basedcompositions, but in general a drying time of from about 1 to 5 minutesat a temperature of about 80°-175° F. (20°-79° C.) will be adequate toinsure that mixing of the two coats is minimized. At the same time, thebase coat film is adequately wetted by the top coat composition so thatsatisfactory intercoat adhesion is obtained. Also, more than one basecoat and multiple top coats may be applied to develop the optimumappearance. Usually between coats, the previously applied base coat ortop coat is flashed, that is, exposed to ambient conditions for about 1to 20 minutes.

The clear film-forming composition which forms the transparent top coatis preferably a crosslinkable composition comprising a polyepoxide and apolyacid which comprises a half-ester formed from reacting an acidanhydride with a polyol.

Among the polyepoxides which can be used are epoxy-containing acrylicpolymers which are preferred, epoxy condensation polymers such aspolyglycidyl ethers of alcohols and phenols and certain polyepoxidemonomers and oligomers.

The epoxy-containing acrylic polymer is a copolymer of an ethylenicallyunsaturated monomer having at least one epoxy group and at least onepolymerizable ethylenically unsaturated monomer which is free of epoxygroups.

Examples of ethylenically unsaturated monomers containing epoxy groupsare those containing 1,2-epoxy groups and include glycidyl acrylate,glycidyl methacrylate and allyl glycidyl ether.

Examples of ethylenically unsaturated monomers which do not containepoxy groups are alkyl esters of acrylic and methacrylic acid containingfrom 1 to 20 atoms in the alkyl group. Specific examples of theseacrylates and methacrylates are those mentioned above in connection withthe acrylic polymers for the base coat. Examples of othercopolymerizable ethylenically unsaturated monomers are vinyl aromaticcompounds, nitriles, vinyl and vinylidene halides and vinyl esters suchas those mentioned above. Acid group-containing copolymerizableethylenically unsaturated monomers such as acrylic and methacrylic acidare preferably not used because of the possible reactivity of the epoxyand acid group.

The epoxy group-containing ethylenically unsaturated monomer ispreferably used in amounts of from about 5 to 60, more preferably from20 to 50 percent by weight of the total monomers used in preparing theepoxy-containing acrylic polymer. Of the remaining polymerizableethylenically unsaturated monomers, preferably from 40 to 95 percent,more preferably from 50 to 80 percent by weight of the total monomersare the alkyl esters of acrylic and methacrylic acid.

In preparing the epoxy-containing acrylic polymer, the epoxidefunctional monomers and the other ethylenically unsaturated monomers canbe mixed and reacted by conventional free radical initiated organicsolution polymerization as generally described above.

The epoxy-containing acrylic polymer typically has a number averagemolecular weight between about 1000 and 20,000, preferably 1000 to10,000, and more preferably 1000 to 5000. The molecular weight isdetermined by gel permeation chromatography using a polystyrenestandard. In determining molecular weights in this fashion, it is notthe actual molecular weights which are measured but an indication of themolecular weight as compared to polystyrene. The values which areobtained are commonly referred to as polystyrene numbers. However, forthe purposes of this invention, they are referred to as molecularweights.

The epoxy condensation polymers which are used are polyepoxides, thatis, those having a 1,2-epoxy equivalency greater than 1, preferablygreater than 1 and up to about 3.0. Examples of such epoxides arepolyglycidyl ethers of polyhydric phenols and of aliphatic alcohols.These polyepoxides can be produced by etherification of the polyhydricphenol or aliphatic alcohol with an epihalohydrin such asepichlorohydrin in the presence of alkali.

Examples of suitable polyphenols are 2,2-bis(4-hydroxyphenyl)-propane(bisphenol A), 1,1-bis(4-hydroxyphenyl)ethane and2-methyl-1,1-bis(4-hydroxyphenyl)propane. Examples of suitable aliphaticalcohols are ethylene glycol, diethylene glycol, 1,2-propylene glycoland 1,4-butylene glycol. Also, cycloaliphatic polyols such as1,2-cyclohexanediol, 1,4-cyclohexanediol,1,2-bis(hydroxymethyl)cyclohexane and hydrogenated bisphenol A can alsobe used.

Besides the epoxy-containing polymers described above, certainpolyepoxide monomers and oligomers can also be used. Examples of thesematerials are described in U.S. Pat. No. 4,102,942 in column 3, lines1-16. Specific examples of such low molecular weight polyepoxides are3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate andbis(3,4-epoxy-6-methylcyclohexyl-methyl) adipate. These materials arealiphatic polyepoxides as are the epoxy-containing acrylic polymers. Asmentioned above, the epoxy-containing acrylic polymers are preferredbecause they result in products which have the best combination ofcoating properties, i.e., smoothness, gloss, durability and solventresistance. Such polymers have been found to be particularly good in theformulation of clear coats for color-plus-clear applications.

The polyepoxide is present in the liquid crosslinkable composition inamounts of about 10 to 90, preferably from 25 to 75 percent by weightbased on total weight of resin solids.

The polyacid contains two or more acid groups per molecule which arereactive with the polyepoxide to form a crosslinked coating as indicatedby its resistance to organic solvent. It comprises a half-ester formedfrom reacting an acid anhydride with a polyol. The acid functionality ispreferably carboxylic acid, although acids such as sulfonic acid may beused but their use is not preferred. The half-esters are relatively lowin molecular weight and quite reactive with epoxies enabling theformulation of high solids fluid compositions while maintainingoutstanding properties such as gloss and distinctness of image.

The half-ester is obtained by reaction between a polyol and a 1,2-acidanhydride under conditions sufficient to ring open the anhydride formingthe half-ester with substantially no polyesterification occurring. Suchreaction products are of relatively low molecular weight with narrowmolecular weight distributions and provide lower volatile organiccontents in the coating composition while still providing for excellentproperties in the resultant coating. By substantially nopolyesterification occurring means that the carboxyl groups of theanhydride are not esterified by the polyol in a recurring manner. Bythis is meant that less than 10, preferably less than 5 percent byweight polyester is formed.

Two reactions may occur in combining the anhydride and the polyoltogether under suitable reaction conditions. The desired reaction modeinvolves ring opening the anhydride ring with hydroxyl, i.e., ##STR1##where X is the residue of the polyol after reaction with the1,2-dicarboxylic acid anhydride, R is an organic moiety associated withthe anhydride and A is equal to at least 2.

Subsequently, carboxyl groups formed by opening of the anhydride ringmay react with hydroxyl groups to give off water via a condensationreaction. This latter reaction is not desired since it can lead to apolycondensation reaction resulting in products with higher molecularweights.

To achieve the desired reaction, the 1,2-acid anhydride and polyol arecontacted together usually by mixing the two ingredients together in areaction vessel. Preferably, reaction is conducted in the presence of aninert atmosphere such as nitrogen and in the presence of a solvent todissolve the solid ingredients and/or to lower the viscosity of thereaction mixture. Examples of suitable solvents are high boilingmaterials and include, for example, ketones such as methyl amyl ketone,diisobutyl ketone, methyl isobutyl ketone; aromatic hydrocarbons such astoluene and xylene; as well as other organic solvents such as dimethylformamide and N-methyl-pyrrolidone.

For the desired ring opening reaction and half-ester formation, a1,2-dicarboxylic anhydride is used. Reaction of a polyol with acarboxylic acid instead of an anhydride would require esterification bycondensation eliminating water which would have to be removed bydistillation. Under these conditions this would promote undesiredpolyesterification. Also, the reaction temperature is preferably low,that is, no greater than 135° C., preferably less than 120° C., andusually within the range of 70°-135° C., preferably 90°-120° C.Temperatures greater than 135° C. are undesirable because they promotepolyesterification, whereas temperatures less than 70° C. areundesirable because of sluggish reaction.

The time of reaction can vary somewhat depending principally upon thetemperature of reaction. Usually the reaction time will be from as lowas 10 minutes to as high as 24 hours.

The equivalent ratio of anhydride to hydroxy on the polyol is preferablyat least about 0.8:1 (the anhydride being considered monofunctional) toobtain maximum conversion to the desired half-ester. Ratios less than0.8:1 can be used but such ratios result in increased formation of lesspreferred half-esters.

Among the anhydrides which can be used in the formation of the desiredpolyesters are those which exclusive of the carbon atoms and theanhydride moiety contain from about 2 to 30 carbon atoms. Examplesinclude aliphatic, including cycloaliphatic, olefinic and cycloolefinicanhydrides and aromatic anhydrides. Substituted aliphatic and aromaticanhydrides are also included within the definition of aliphatic andaromatic provided the substituents do not adversely affect thereactivity of the anhydride or the properties of the resultantpolyester. Examples of substituents would be chloro, alkyl and alkoxy.Examples of anhydrides include succinic anhydride, methylsuccinicanhydride, dodecenyl succinic anhydride, octadecenylsuccinic anhydride,phthalic anhydride, tetrahydrophthalic anhydride,methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, alkylhexahydrophthalic anhydrides such as methylhexahydrophthalic anhydride,tetrachlorophthalic anhydride, endomethylene tetrahydrophthalicanhydride, chlorendic anhydride, itaconic anhydride, citraconicanhydride and maleic anhydride.

Among the polyols which can be used are those which contain from about 2to 20 carbon atoms. Preferred are diols, triols and mixtures thereof.Examples include polyols containing from 2 to 10 carbon atoms. Examplesinclude aliphatic polyols such as ethylene glycol, 1,2-propanediol,1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, glycerol,1,2,3-butanetriol, 1,6-hexanediol, neopentyl glycol, diethylene glycol,dipropylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane,2,2,4-trimethylpentane-1,3-diol, pentaerythritol and1,2,3,4-butanetetrol. Aromatic polyols such as bisphenol A andbis(hydroxymethyl) xylene can also be used.

The half-ester is present in the coating composition in amounts of about10 to 90, preferably 25 to 75 percent by weight based on total weight ofresin solids.

The polyepoxide and the half-ester are essential ingredients in thecrosslinkable composition. However, there are optional materials whichare preferred ingredients in the compositions. These include an acidfunctional acrylic polymer and an anhydride.

The acid functional acrylic polymer provides sag control. The preferredclear film-forming compositions are high solids compositions and have atendency to sag when applied to vertical surfaces. The acid functionalacrylic polymer surprisingly provides sag control to the compositions.The acid functional acrylic polymers are the reaction product of anethylenically unsaturated polymerizable carboxylic acid such as acrylicacid or methacrylic acid and ethylenically unsaturated polymerizablemonomers other than said acids. These products are non-gelled andtypically will have number average molecular weights as determined bygel permeation chromatography using a polystyrene standard of from about500 to 5000, preferably 700 to 3000. The preferred reaction productswill also have a uniform molecular weight distribution which isevidenced by polydispersity values which are preferably less than 4,more preferably from 2 to 3. The polydispersity value is the ratio ofthe weight average molecular weight to the number average molecularweight each being determined by gel permeation chromatography using apolystyrene standard as described above.

The amount of acid functional acrylic polymer which is used can varyfrom 0 to 50, preferably from 10 to 20 percent by weight based on totalweight of resin solids.

The polyepoxide-polyacid compositions also preferably contain ananhydride, preferably an anhydride which is a liquid at 25° C. Thepresence of such an anhydride in the compositions provides an improvedcure response. Examples of suitable anhydrides include alkyl-substitutedhexahydrophthalic anhydrides such as methyl hexahydrophthalic anhydrideand dodecenyl succinic anhydride. The amount of the anhydride which isused can vary from 0 to 40, preferably from 5 to 25 percent by weightbased on total weight of resin solids.

Optionally, the crosslinkable composition can contain silanefunctionality which can be incorporated into the composition by using areactive silane group-containing material such asgamma-methacryloxypropyltrimethoxysilane ormercaptopropyltrimethoxysilane which can be used in the preparation ofthe epoxy group-containing acrylic polymer. Such materials coreact withthe polymerizing monomers or polymers forming a polymer with silanecuring groups. Alternately, a silane group-containing material such asmethyltrimethoxysilane can be included in the composition. The silanefunctionality results in lower temperature cure.

The equivalent ratio of carboxyl to epoxy in the clear film-formingcompositions is preferably adjusted so that there are about 0.3 to 3.0,preferably from 0.8 to 1.5 equivalents of carboxyl (anhydride beingconsidered monofunctional) per equivalent of epoxy.

The compositions will also preferably contain catalysts to acceleratethe cure of the epoxy and acid groups. Examples of suitable catalystsinclude organic amines and quaternary ammonium compounds such aspyridine, piperidine, dimethylaniline, diethylenetriamine,tetramethylammonium chloride, tetramethylammonium acetate,tetramethylbenzylammonium acetate, tetrabutylammonium fluoride, andtetrabutylammonium bromide. The amount of catalyst is typically from 0to 10, preferably 0.5 to 3 percent by weight based on resin solids.

The polyepoxide-polyacid compositions are preferably formulated intohigh solids coating compositions. That is, these coating compositionscontain greater than 50 percent, most preferably greater than 60 percentby weight resin solids. The solids content is determined by heating thecomposition to 105°-110° C. for 1 to 2 hours to drive off the volatilematerial. The compositions are preferably liquid high solidscompositions, but they can also be formulated as powder coatings.

Also, optional ingredients such as auxiliary curing agents such asaminoplast resins, plasticizers, anti-oxidants, and UV light absorberscan be included in the composition. These ingredients typically arepresent in amounts of up to 25 percent by weight based on total resinweight.

Besides the polyepoxide-polyacid compositions described above, the clearcoat can be formulated with conventional resinous binders such as theacrylic polymers, polyesters, alkyds and polyurethanes described abovein connection with the base coats. In this instance, the base coat willcontain polyepoxide-polyacid compositions.

The clear top coat composition can be applied to the base-coatedsubstrate by any of the conventional coating techniques such asbrushing, spraying, dipping or flowing, but it is preferred that sprayapplications be used since this gives the best gloss. Any of the knownspray techniques may be employed such as compressed air spraying,electrostatic spraying and either manual or automatic methods.

After application of the top coat composition to the base coat, thecoated substrate is heated to cure the coating layers. In the curingoperation, solvents are driven off and the film-forming material of thetop coat and/or of the base coat is crosslinked with the aid of anycrosslinking agents present. The heating or curing operation is usuallycarried out at a temperature in the range of from 160°-350° F. (71°-177°C.) but if needed lower or higher temperatures may be used dependingupon whether it is sufficient to activate any necessary crosslinkingmechanisms. The thickness of the top coat is usually from about 1 to 5,preferably 1.2 to 3 mils.

The invention will be further described by reference to the followingexamples. Unless otherwise indicated, all parts are by weight.

EXAMPLES

The following examples (Examples A-E) show the preparation ofepoxy-containing acrylic polymers, polyacid half-esters and anacid-containing acrylic polymer.

EXAMPLE A

An epoxy-containing acrylic polymer was prepared from the followingmixture of ingredients:

    ______________________________________                                                        Weight    Percentage                                          Ingredients     in Grams  by Weight                                           ______________________________________                                        Glycidyl methacrylate                                                                           320.0   40                                                  Methyl methacrylate                                                                             160.0   20                                                  Butyl acrylate    160.0   20                                                  Butyl methacrylate                                                                              160.0   20                                                  VAZO-67.sup.1      24.0   3.0 (on monomers)                                   Tertiary-butyl perbenzoate                                                                       16.0   2.0 (on monomers)                                   Tertiary-butyl perbenzoate                                                                       4.0    0.5 (on monomers)                                   (post-addition)                                                               Tertiary-butyl perbenzoate                                                                       4.0    0.5 (on monomers)                                   (post-addition)                                                               ______________________________________                                         .sup.1 Alpha, alphadimethylazobis(isobutyronitrile) available from E. I.      duPont de Nemours and Company.                                           

Xylene (415.3 grams) was charged to a suitable reactor and heated toreflux to remove water through a Dean-Stark trap. The glycidylmethacrylate, methyl methacrylate, butyl acrylate and butyl methacrylatewere mixed together. The VAZO-67, first portion of tertiary-butylperbenzoate and 100 grams of xylene were also premixed together. Thepremixture of vinyl monomers and the premixture of initiators were addedsimultaneously to the reaction vessel over a period of about 3 hourswhile maintaining the reaction temperature at reflux. At the completionof the addition, the reaction mixture was held at reflux for one hourfollowed by the addition of the second portion of tertiary-butylperbenzoate and 25 grams of xylene. The reaction mixture was held forone hour at reflux followed by the addition of the third portion oftertiary-butyl perbenzoate and 25 grams of xylene. The reaction mixturewas held for two hours at reflux followed by cooling to roomtemperature. The reaction mixture had a solids content of about 60percent and a number average molecular weight of 1456 as determined bygel permeation chromatography using a polystyrene standard.

EXAMPLE B

An apoxy-containing acrylic polymer containing silane functionality wasprepared from the following mixture of ingredients:

    ______________________________________                                        Kettle Charge                                                                 Ingredients       Parts by Weight (in grams)                                  ______________________________________                                        Xylene            480.0                                                       ______________________________________                                        Charge I                                                                                       Parts by Weight                                                                           Percentage                                       Ingredients      (in grams)  by Weight                                        ______________________________________                                        Glycidyl methacrylate                                                                          896.0       40.0                                             Methyl methacrylate                                                                            560.0       25.0                                             Butyl acrylate   448.0       20.0                                             Gamma-methacryloxy-                                                                            336.0       15.0                                             propyltrimethoxysilane                                                        ______________________________________                                        Ingredients       Parts by Weight (in grams)                                  ______________________________________                                        Charge II                                                                     Xylene            288.0                                                       VAZO-67           112.0                                                       Charge III                                                                    Xylene            144.0                                                       Mercaptopropyltrimethoxysilane                                                                  112.0                                                       Charge IV                                                                     Xylene             24.0                                                       VAZO-67            8.96                                                       Charge V                                                                      Xylene             24.0                                                       VAZO-67            8.96                                                       ______________________________________                                    

The kettle charge was heated to reflux in a suitable reactor to removewater through a Dean-Stark trap. Charges I, II and III were addedsimultaneously over the period of three hours while maintaining thereaction mixture at reflux. Charge IV was added and the reaction mixtureheld at reflux for one hour, followed by the addition of Charge V andholding the reaction mixture at reflux for one hour, followed by coolingto room temperature. The reaction mixture had a solids content (150° C.)of 67.7 percent and a number average molecular weight of 1435 asdetermined by gel permeation chromatography using a polystyrenestandard.

EXAMPLE C

An epoxy-containing acrylic polymer was prepared from the followingmixture of ingredients:

    ______________________________________                                        Kettle Charge                                                                 Ingredients   Parts by Weight                                                 ______________________________________                                        Butyl acetate 906.0                                                           ______________________________________                                        Charge I                                                                                      Parts by Weight                                                                           Percentage                                        Ingredients     (in grams)  By Weight                                         ______________________________________                                        Glycidyl methacrylate                                                                         510.0       30                                                Methyl methacrylate                                                                           595.0       35                                                Butyl acrylate  170.0       10                                                Butyl methacrylate                                                                            425.0       25                                                Butyl acetate   200                                                           ______________________________________                                        Ingredients  Parts by Weight (in grams)                                       ______________________________________                                        Charge II                                                                     VAZO 67      59.5                                                             Butyl acetate                                                                              180.0                                                            Charge III                                                                    VAZO 67       8.5                                                             Butyl acetate                                                                              40.0                                                             ______________________________________                                    

The kettle charge was heated in a suitable reactor to reflux to removewater through a Dean-Stark trap. Charges I and II were addedsimultaneously over the period of about three hours while maintainingthe reaction mixture at reflux. At the conclusion of the addition ofCharges I and II, the reaction mixture was held for one hour at refluxfollowed by the addition of Charge III over a 30-minute period. Thereaction mixture was held at reflux for an additional hour followed bycooling to room temperature. The volatile materials in the reactionmixture were then removed by heating under vacuum to a solids content of99.8 percent. The reaction product had a number average molecular weightof 4048.

EXAMPLE D

A polyacid half-ester of 1,6-hexanediol-methylhexahydrophthalicanhydride was prepared from the following mixture of ingredients:

    ______________________________________                                        Ingredients         Parts by Weight (in grams)                                ______________________________________                                        1,6-Hexanediol      590.0                                                     Methylhexahydrophthalic anhydride                                                                 1680.0                                                    Methyl isobutyl ketone                                                                            972.9                                                     ______________________________________                                    

The 1,6-hexanediol and the methyl isobutyl ketone were charged to areaction vessel and heated under a nitrogen atmosphere to 115° C. Themethylhexahydrophthalic anhydride was charged over a 2-hour period whilemaintaining the reaction temperature between 112°-117° C. The reactionmixture was held at this temperature for about 3 to 4 hours to a stalledacid value, i.e., acid value remained essentially constant. The reactionmixture was then cooled to room temperature and found to have a solidscontent measured at 110° C. of 68.0 percent and an acid value of 176.

EXAMPLE E

A polyacid half-ester of trimethylolpropane and methylhexahydrophthalicanhydride was prepared from the following mixture of ingredients:

    ______________________________________                                        Ingredients         Parts by Weight (in grams)                                ______________________________________                                        Trimethylolpropane  1341.0                                                    Methylhexahydrophthalic anhydride                                                                 5040.0                                                    Methyl isobutyl ketone                                                                            2734.7                                                    ______________________________________                                    

The trimethylolpropane and the methyl isobutyl ketone were charged to asuitable reaction vessel and heated under a nitrogen atmosphere to 115°C. The methylhexahydrophthalic anhydride was charged over a 2-hourperiod while maintaining the temperature between 112°-117° C. Thereaction mixture was held at this temperature for about 3 hours. Thereaction product was then cooled to room temperature and found to have asolids content measured at 110° C. of 69 percent and an acid value of200.3.

EXAMPLE F

An acid functional acrylic polymer was prepared from the followingingredients:

    ______________________________________                                        Kettle Charge                                                                 Ingredients     Parts by Weight (in grams)                                    ______________________________________                                        Half-ester prepared as                                                                        2571.3                                                        described in Example D                                                        ______________________________________                                        Feed A                                                                                        Parts by Weight                                               Ingredients     (in grams)  Percent                                           ______________________________________                                        2-Ethylhexyl acrylate                                                                         2160        40                                                Styrene         1080        20                                                Methacrylic acid                                                                              1080        20                                                Butyl methacrylate                                                                            1053        19.5                                              Methyl methacrylate                                                                            27         0.5                                               Di-tertiary-butyl peroxide                                                                     54         1% based on                                                                   monomers                                          ______________________________________                                        Feed                                                                          Ingredients     Parts by Weight (in grams)                                    ______________________________________                                        Methyl isobutyl ketone                                                                        1800                                                          ______________________________________                                    

The kettle charge was heated under a nitrogen atmosphere to reflux.Solvent was distilled and the reaction temperature increased to about240° C. Feed A was added over a period of 30 minutes while maintainingthe temperature between 187° and 200° C. At the completion of Feed A,the reaction mixture was held for 10 minutes at 189° C. Solvent wasdistilled until the reaction temperature reached 220° C. The reactionmixture was then cooled to 120° C. followed by thinning with Feed B. Thereaction mixture was then cooled and found to have a solids content of76.6 percent measured at 110° C., an acid value of 103.5 (theoretical126) and a number average molecular weight of 840.

The following examples (1-6) show the preparation of various clearfilm-forming compositions prepared with the epoxy-containing acrylicpolymers, the various polyacid half-esters and the acid functionalacrylic polymer described above in Examples A through F. The coatingcompositions were then used in a color-plus-clear application.

EXAMPLE 1

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

    ______________________________________                                                          Parts by Weight                                                                           Percent                                         Ingredients       (in grams)  Resin Solids                                    ______________________________________                                        TINUVIN 328.sup.1 3.0         3.0                                             Hexyl acetate.sup.2                                                                             20.0        --                                              Epoxy-containing acrylic                                                                        103.8       60.2                                            polymer of Example A                                                          1,6-Hexanediol-methyl-                                                                          57.5        39.8                                            hexahydrophthalic anhydride                                                   half-ester of Example D                                                       DC-200 10 C.S..sup.3 (10% in xylene)                                                            1.0         0.1                                             ARMEEN DM 12D.sup.4                                                                             2.0         2.0                                             ______________________________________                                         .sup.1 Substituted benzotriazole UV light stabilizer available from           CibaGeigy Corporation.                                                        .sup.2 EXXATE 600 from Exxon Company.                                         .sup.3 Silicone fluid available from the Dow Corning Corporation.             .sup.4 N,N--dimethyldodecylamine catalyst available from AKZO Chemical.  

The formulated coating composition contained 56 percent by weight resinsolids and had a No. 4 Ford cup viscosity of 26.3 seconds.

EXAMPLE 2

A clear film-forming composition, similar to Example 1 but includingmethylhexahydrophthalic anhydride as a cure promoter, was prepared fromthe following mixture of ingredients:

    ______________________________________                                                         Parts by Weight                                                                           Percent                                          Ingredients      (in grams)  Resin Solids                                     ______________________________________                                        TINUVIN 328      3.0         3.0                                              Hexyl acetate    20.0        --                                               Epoxy-containing acrylic                                                                       108.6       63.0                                             polymer of Example A                                                          1,6-Hexanediol-methyl-                                                                         31.4        21.7                                             hexahydrophthalic anhydride                                                   half-ester of Example D                                                       DC-200           1.0         0.1                                              ARMEEN DM 12D    2.0         2.0                                              Methylhexahydrophthalic                                                                        15.3        15.3                                             anhydride                                                                     ______________________________________                                    

The resultant coating composition contained 58 percent by weight resinsolids and had a No. 4 Ford cup viscosity of 25 seconds.

EXAMPLE 3

A clear film-forming composition similar to Example 2 was prepared butwith the trimethylolpropane-methylhexahydrophthalic anhydride half-esterof Example E and also including the diglycidyl ether ofcyclohexanedimethanol. The coating composition was prepared from thefollowing ingredients:

    ______________________________________                                                         Parts by Weight                                                                           Percent                                          Ingredients      (in grams)  Resin Solids                                     ______________________________________                                        TINUVIN 328       3.0         3.0                                             Methyl ethyl ketone                                                                            14.8        --                                               DC-200            1.0         0.1                                             Diglycidyl ether of                                                                            16.8        16.8                                             cyclohexanedimethanol                                                         Methylhexahydrophthalic                                                                        16.5        16.5                                             anhydride                                                                     ARMEEN DM 12D     2.0         2.0                                             Epoxy-containing acrylic                                                                       72.3        41.6                                             polymer of Example A                                                          Trimethylolpropane-methyl-                                                                     35.3        25.1                                             hexahydrophthalic anhydride                                                   half-ester of Example E                                                       ______________________________________                                    

The resultant formulated coating composition contained 65 percent resinsolids and had a No. 4 Ford cup viscosity of 18.1 seconds.

EXAMPLE 4

A clear film-forming composition similar to Example 3 but including theacid functional acrylic polymer of Example F as a flow control agent wasprepared from the following mixture of ingredients:

    ______________________________________                                                         Parts by Weight                                                                           Percent                                          Ingredients      (in grams)  Resin Solids                                     ______________________________________                                        TINUVIN 328       3.0         3.0                                             Methyl ethyl ketone                                                                            17.7        --                                               DC-200            1.0         0.1                                             Diglycidyl ether of                                                                            16.8        16.8                                             cyclohexanedimethanol                                                         Methylhexahydrophthalic                                                                        16.5        16.5                                             anhydride                                                                     ARMEEN DM 12D     2.0         2.0                                             Epoxy-containing acrylic                                                                       64.5        37.4                                             polymer of Example A                                                          Trimethylolpropane-methyl-                                                                     21.6        14.7                                             hexahydrophthalic anhydride                                                   half-ester of Example E                                                       Acid-containing acrylic                                                                        18.6        14.5                                             polymer of Example F                                                          ______________________________________                                    

The formulated coating composition contained 65 percent by weight resinsolids and had a No. 4 Ford cup viscosity of 24.2 seconds.

EXAMPLE 5

A clear film-forming composition containing the silane group-containing,epoxy group-containing acrylic polymer of Example B andtrimethylolpropane-methylhexahydrophthalic anhydride half-ester ofExample E was prepared from the following ingredients:

    ______________________________________                                                            Parts                                                                         by Weight Percent                                         Ingredients         (in grams)                                                                              Resin Solids                                    ______________________________________                                        TINUVIN 328          3.0      3.0                                             Xylene              16.7      --                                              Hexyl acetate       10.0      --                                              Silane and epoxy group-containing                                                                 103.4     72.4                                            acrylic polymer of Example B                                                  Trimethylolpropane-methyl-                                                                        39.4      27.6                                            hexahydrophthalic anhydride                                                   half-ester of Example E                                                       DC-200               1.0      0.1                                             Dibutyltin dilaurate                                                                               3.0      3.0                                             Tetrabutylammonium bromide (25%                                                                   30.0      7.5                                             by weight in butanol)                                                         ______________________________________                                    

EXAMPLE 6

A pigmented base coat composition containing aluminum flakepigmentation, the epoxy-containing acrylic polymer of Example A and the1,6-hexanediol-methylhexahydrophthalic anhydride half-ester of Example Dwas prepared from the following mixture of ingredients:

    ______________________________________                                                        Parts by Weight                                                                           Resin   Pigment                                   Ingredients     (in grams)  Solids  Solids                                    ______________________________________                                        TINUVIN 328      3.0         3.0                                              Hexyl acetate   60.9        --                                                Flow control agent.sup.1                                                                      45.4        20.0                                              Epoxy-containing acrylic                                                                      81.4        47.2                                              polymer of Example A                                                          1,6-Hexanediol-methyl-                                                                        47.5        32.8                                              hexahydrophthalic anhydride                                                   half-ester of Example D                                                       ARMEEN DM 12D    2.0         2.0                                              Aluminum flake.sup.2                                                                          15.4        --      10.0                                      ______________________________________                                         .sup.1 Polymeric microparticle prepared in accordance with Example 11 of      U.S. Pat. No. 4,147,688.                                                      .sup.2 65 Percent by weight nonleafing aluminum flakes and hydrocarbon        solvent available from Alcoa Company as L7575.                           

The ingredients were mixed in the order indicated at low shear with goodagitation to form the pigmented base coating composition.

The clear film-forming compositions of Examples 1-5 were applied to boththe pigmented base coat of Example 6 and to a light blue metallicwater-based base coat to form color-plus-clear composite coatings oversteel substrates. The light blue metallic base coat was available fromImperial Chemical Industries Ltd. as M-979. This product was prepared inaccordance with the teachings of U.S. Pat. No. 4,403,003.

The base coats were spray applied by hand to steel panels at atemperature of about 25° C. A 3-minute flash at 180° F. (82° C.) wasallowed between coats for the water-base base coat. The solvent-basebase coat was given a 90-second flash at ambient conditions. The totalfilm thickness for the base coat of Example 6 was about 0.6 mil and forthe water-base base coat about 0.3 mil.

After application of the second base coat, two coats of the variousclear coat compositions described in Examples 1-5 were spray appliedwith an automatic spraying device. The two coats were applied wet-on-wetto the basecoated panels with a 2-minute flash off at room temperaturebetween the coats. After a final 2-minute flash off, the panels werethen baked in both the horizontal and vertical positions (90° fromhorizontal unless otherwise indicated) at 250° F. (121° C.) for 30minutes unless otherwise indicated. The properties of the compositecoating are reported in the table below and are seen to have excellentgloss and distinctness of image.

                                      TABLE                                       __________________________________________________________________________    Properties of Color + Clear Coatings                                          __________________________________________________________________________    Base Coat     Ex. 6                                                                            Ex. 6                                                                            Ex. 6                                                                            Ex. 6                                                                            Water Base                                                                          Water Base                                                                          Water Base                                                                          Water Base                                                                          Water Base                  Clear Coat    Ex. 1                                                                            Ex. 2                                                                            Ex. 3                                                                            Ex. 4                                                                            Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5.sup.7                 Clear Coat Film                                                                             1.7                                                                              1.6                                                                              1.8                                                                              1.5                                                                              1.7   1.6   1.8   1.5   2.1                         Thickness in mils                                                             20° Gloss.sup.1                                                                      88/88                                                                            89/88                                                                            89/89                                                                            90/89                                                                            88/87 88/88 88/87 89/88 86                          Horizontal/Vertical                                                           DOI.sup.2 Horizontal/Vertical                                                               85/75                                                                            85/75                                                                            95/70                                                                            90/70                                                                            85/80 90/85 100/85                                                                              95/90 70                          Adhesion.sup.3                                                                              2  1-2                                                                              5  5  5     5     5     5     --                          Tukon Hardness Number.sup.4                                                                 -- -- -- -- 2.15  7.26  8.24  5.75  3-4                         Solvent Resistance.sup.5                                                                    poor                                                                             fair                                                                             good                                                                             good                                                                             --    --    --    --    good                        Sag Resistance.sup.6                                                                        good                                                                             good                                                                             poor                                                                             good                                                                             good  excellent                                                                           poor  good  --                          __________________________________________________________________________     .sup.1 Measured with a 20 degree gloss meter manufactured by Gardner          Instrument Company. Measurements were made on the panels which were baked     in both the vertical and horizontal positions.                                .sup.2 Determined on DoriGon Meter D476 manufactured by Hunter                Laboratories.                                                                 .sup.3 Crosshatch adhesion determined by ASTM D3359.                          .sup.4 Determined by ASTM E384.                                               .sup.5 Solvent resistance determined by rubbing with normal hand pressure     back and forth (double rub) with a xylenesaturated cloth. A good rating       was given if the coating withstood 20 double rubs without marring the         surface. A fair rating was given for a marred surface, and a poor rating      was given when the coating was completely removed.                            .sup.6 Sag resistance was determined on the panels which were baked in th     vertical position. An excellent rating indicated essentially no sagging o     dripping of the coating. Sag is indicated by a considerably thicker film      developing on the bottom of the panel. A good rating indicated some           sagging. A poor rating indicated heavy sagging or dripping.                   .sup.7 Gloss and DOI for this example measured after the clear coat was       cured in the horizontal position for 30 minutes at 180° F.             (82° C.).                                                         

EXAMPLE 7

A clear film-forming powder coating composition was prepared by mixingtogether the following ingredients:

    ______________________________________                                        Ingredients       Parts by Weight (in grams)                                  ______________________________________                                        TINUVIN 900.sup.1 3.0                                                         IRGANOX 1010.sup.2                                                                              1.0                                                         Benzoin           0.5                                                         FC-430.sup.3      1.0                                                         Trimethylolpropane-methyl-                                                                      30.8                                                        hexahydrophthalic anhydride                                                   half-ester of Example D.sup.4                                                 Epoxy-containing acrylic                                                                        69.2                                                        polymer of Example C                                                          ______________________________________                                         .sup.1 Hindered UV light stabilizer available from Ciba Geigy Corp.           .sup.2 Hindered phenol antioxidant available from Ciba Geigy Corp.            .sup.3 Fluorocarbon surfactant available from the 3M Corp.                    .sup.4 Solvent stripped to 99.8 percent solids.                          

The ingredients mentioned above were blended together in a planetarymixer, extruded, chilled on a chill roll, flaked and ground into a finepowder in a micromill and then passed through a 100-mesh screen to formthe final powder coating composition.

The powder coating composition was applied to the base coat of Example6. The base coat was spray applied by hand to steel panels at atemperature of 25° C. Two coats were applied with a 90-second flash atambient conditions between coats. The total film thickness was 0.6 mil.After application of the second base coat, two coats of the clear powdercoating composition were electrostatically sprayed onto the base coatvia a wet-on-wet application. The composite coating was then baked at350° F. (177° C.) for 30 minutes. The clear coat had a thickness of 2.6mils, a 20° gloss of 80, a DOI of 45 and a crosshatch adhesion value of5, a Tukon hardness number of 10.0 and good solvent resistance.

We claim:
 1. A process for applying a composite coating to a substratewhich comprises applying to the substrate a colored film-formingcomposition to form a base coat and applying to said base coat a clearfilm-forming composition to form a transparent top coat over the basecoat comprising as the clear film-forming composition and/or as thecolored film-forming composition a crosslinkable composition comprisinga polyepoxide and a polyacid curing agent which is a half-ester formedfrom reacting an acid anhydride with a polyol; there being from 0.3 to 3equivalents of acid for each equivalent of epoxy.
 2. The process ofclaim 1 in which the crosslinkable composition is used as the clearfilm-forming composition.
 3. The process of claim 1 in which thepolyepoxide is a copolymer of a monoethylenically unsaturated monomerhaving at least one epoxy group and at least one monoethylenicallyunsaturated monomer which is free of epoxy groups.
 4. The process ofclaim 3 in which the copolymer has a number average molecular weight ofbetween 500 and 20,000.
 5. The process of claim 4 in which the copolymeris a copolymer of glycidyl acrylate or methacrylate with at least oneother copolymerizable ethylenically unsaturated monomer.
 6. The processof claim 5 in which the other copolymerizable ethylenically unsaturatedmonomer comprises at least in part an alkyl ester of acrylic ormethacrylic acid containing from 1 to 20 carbon atoms in the alkylgroup.
 7. The process of claim 5 in which the glycidyl acrylate ormethacrylate comprises from 5 to 60 percent of the monomers used inpreparing the epoxy-containing acrylic polymer.
 8. The process of claim3 in which the epoxy group-containing acrylic polymer is present in thecrosslinkable composition in amounts of 10 to 90 percent by weight basedon total weight of resin solids.
 9. The process of claim 1 in which thecrosslinkable composition contains hydrolyzable silane groups.
 10. Theprocess of claim 3 in which the crosslinkable composition containshydrolyzable silane groups in the epoxy-containing acrylic polymer. 11.The process of claim 1 in which the half-ester is of the structure:##STR2## where X is the residue of a polyol after reaction with the1,2-dicarboxylic acid anhydride, R is an organic moiety associated withthe anhydride, and A is equal to at least
 2. 12. The process of claim 11in which the polyol is a diol, triol, or mixture thereof.
 13. Theprocess of claim 12 in which the polyol is selected from the classconsisting of trimethylolpropane, neopentyl glycol and 1,6-hexanediol.14. The process of claim 11 in which the 1,2-dicarboxylic acid anhydrideis selected from the class consisting of hexahydrophthalic anhydride andalkyl-substituted hexahydrophthalic anhydrides.
 15. The process of claim1 in which the half-ester is present in amounts of 10 to 90 percent byweight based on total weight of resin solids.
 16. The process of claim 1in which the crosslinkable composition contains an acid functionalacrylic polymer.
 17. The process of claim 16 in which the acidfunctional acrylic polymer has a number average molecular weight of 500to
 5000. 18. The process of claim 16 in which the acid functionalacrylic polymer is prepared from a mixture of acrylic monomers whichincludes from 10 to 60 percent by weight of an acid functional acrylicmonomer; the percentage by weight being based on total weight of acrylicmonomers.
 19. The process of claim 16 in which the acid functionalacrylic polymer is present in the crosslinkable composition in amountsof from 0 to 50 percent by weight, based on total weight of resinsolids.
 20. The process of claim 1 in which the crosslinkablecomposition contains an anhydride.
 21. The process of claim 20 in whichthe anhydride is a liquid at 25° C.
 22. The process of claim 21 in whichthe anhydride is an alkyl hexahydrophthalic anhydride.
 23. The processof claim 20 in which the anhydride is present in amounts of 0 to 40percent by weight based on total weight of resin solids.
 24. The processof claim 1 in which the crosslinkable composition has a resin solidscontent of at least 50 percent.
 25. A substrate coated in accordancewith the process of claim
 1. 26. A substrate coated in accordance withthe process of claim
 16. 27. A substrate coated in accordance with theprocess of claim 20.